This project will further characterize and, for the first time, compare electroencephalographic sleep in elderly patients with depression and primary degenerative dementia, the two most common neuropsychiatric disorders of old age. Pilot data indicate significant differences between groups in REM sleep measures, notably, higher REM sleep density and altered temporal distribution of REM in depression, including a shorter REM sleep latency. These differences in REM sleep timing and density may be relate to increased cholinergic activity/sensitivity in depression and diminished cholinergic activity in dementia. Three groups of 25 subjects each (aged 60-75) will have three consecutive nights of EEG sleep studies, followed by a multiple sleep latency test (to measure daytime sleepiness). Plasma and RBC choline levels will be drawn at the conclusion of each nocturnal polysomnogram. Group 1 will be limited to outpatients with primary major depression, group 2, to non-depressed outpatients with primary degenerative dementia; and group 3, to normal controls. The specific aims of this research are to determine if there are reliable differences in the EEG sleep of elderly depressed and demented subjects which could then be further tested in a prospective longitudinal study of patients with mixed symptoms of depression and cognitive impairment to establish the predictive validity of these measure; to establish whether differences in REM sleep are correlated with RBC-to-plasma choline ratio; and to determine whether there is abnormal daytime sleepiness in elderly depressed and demented subjects and its relation to measures of nocturnal sleep fragmentation, sleep-disordered breathing, and cognitive impairment.